Semiconductor device utilizing a metal gate material such as tungsten and method of manufacturing the same

ABSTRACT

Known drawbacks associated with use of tungsten as a gate material in a semiconductor device are prevented. A gate oxide layer, a polysilicon layer, and a nitride layer are sequentially formed on a semiconductor substrate having a isolation layer for defining the active region. A recess is defined by etching the nitride layer. A metal nitride layer is formed in the recess in an U shape, and then a metal layer is formed to bury the recess. A hard mask layer is formed for defining a gate forming region on the nitride layer, the metal nitride layer, and the metal layer. A metal gate is formed by etching the nitride layer, the polysilicon layer, and the gate oxide layer using the hard mask layer as an etch barrier.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, in general, to a semiconductor devicehaving a gate, and more particularly to a semiconductor device forpreventing the drawbacks due to the use of tungsten as the gatematerial.

2. Description of the Related Art

For increasingly high integration of the semiconductor devices, thechannel length of a transistor is significantly shortened and thethreshold voltage of the transistor is set to decrease abruptly, all ofwhich contribute to the so-called “short channel effect” to become moreserious. In an effort to increase a channel length of a transistor, manyresearches for a recess gate were conducted, according to which a recessis defined on a silicon substrate to increase a transistor channellength. A recess gate forming method increases a channel length byforming a gate in a recess; thus, the short channel effect can bereduced when it is compared to a conventional planar gate structure.

Therefore, as the integration degree of a semiconductor deviceincreases, a material having a very low resistance (such as tungsten) isknown for use as a gate material when forming a recess gate in order todecrease the resistance of the gate.

Hereafter, a conventional method of forming a recess gate in asemiconductor device which uses tungsten as the gate material isdescribed with reference to FIGS. 1A through 1D.

Referring to FIG. 1A, a isolation layer 2 is formed in a semiconductorsubstrate 1 through a shallow trench isolation (STI) process to definethe active region. Then, an oxide layer 3 and a hard mask layer 4 aresequentially deposited on the substrate 1, which are going to be used asan etch barrier layer for forming a recess gate.

Referring to FIG. 1B, the hard mask layer 4 and the oxide layer 3 aresequentially etched to formed an etch mask through which a plurality ofthe gate forming regions of the substrate 1 are exposed. Then, theexposed portions of the substrate 1 are etched using the etch maskformed by the etched hard mask layer 4 and the oxide layer 3, to formrecesses 5. After forming the recesses 5, the hard mask layer 4 and theoxide layer 3 are sequentially removed. As shown in FIG. 1B, Here, whenetching the substrate 1 to define the recess 5, the portions in theisolation layer 2 of the substrate 1 are also partially etched.

Referring to FIG. 1C, a gate oxide layer 6 is formed on the surface ofthe active region of the substrate 1 including the surface of therecesses 5 in the active region. Then, a polysilicon layer 7, a tungstennitride layer 8, a tungsten layer 9, and a gate hard mask layer 10 aresequentially formed on the surface of the resultant substrate 1, andthese layers are then patterned to form tungsten gates 11 on therecesses 5.

Referring to FIG. 1D, a gate selective oxidation process is performed onthe resultant substrate 1 in order to form a re-oxidation layer 12 onthe surface of the etched polysilicon layer 7 and on the surface of theactive region of the substrate 1 as shown in FIG. 1D. Thereafter, inorder to prevent the abnormal oxidization of tungsten by a subsequentprocess, a gate capping nitride layer 13 is formed on the entire surfaceof the resultant substrate 1 including the tungsten gate 11.

However, when tungsten is used as the gate material, if process andequipment conditions become unstable while the gate selectiveoxidization process is conducted, the possibility of an abnormaloxidization phenomenon to occur increases, in which a re-oxidation layeris abnormally formed on tungsten. Also, due to the fact that oxygen canintrude through the tungsten layer 9 to form an insulation layer betweentungsten 9 and polysilicon 7 while conducting the gate selectiveoxidization process and due to issues such as the contamination oftungsten, etc., a detrimental defect can be caused when operating thesemiconductor device.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made in an effort to solvethe problems occurring in the related art, and one of many objects ofthe present invention is to provide a semiconductor device which canprevent a drawback due to the use of tungsten as gate material, and amethod for manufacturing the same.

In order to achieve the above object, according to one aspect of thepresent invention, there is provided a semiconductor device comprising asemiconductor substrate having a isolation layer for defining an activeregion; and a metal gate formed on the active region of the substrateand capped on side surfaces thereof by a nitride layer.

According to another aspect of the present invention, a recess isdefined on a portion of the active region of the semiconductor substrateat which a gate is formed.

According to another aspect of the present invention, a metal nitridelayer is intervened between a metal layer constituting the metal gateand the nitride layer.

According to another aspect of the present invention, the metal nitridelayer is formed to surround side surfaces and a bottom surface of themetal layer.

According to another aspect of the present invention, the metal gateincludes a gate oxide layer and a polysilicon layer which are stacked inthe shape of a pattern; a metal nitride layer formed on the polysiliconlayer in the shape of U; a metal layer buried in the metal nitridelayer; the nitride layer formed on sides of the metal nitride layer; anda hard mask layer formed on the nitride layer, the metal nitride layerand the metal layer in the shape of a pattern.

According to another aspect of the present invention, an entire width ofthe combined nitride layer, metal nitride layer and metal layer is thesame as a width of the polysilicon layer.

According to another aspect of the present invention, the metal nitridelayer comprises a tungsten nitride layer, the metal layer comprises atungsten layer, and the hard mask layer comprises a nitride layer.

According to another aspect of the present invention, the semiconductordevice further comprising source and drain regions formed in the activeregion of the substrate at sides of the metal gate.

In order to achieve the above object, according to another aspect of thepresent invention, there is provided a method for manufacturing asemiconductor device, comprising the steps of forming sequentially agate oxide layer, a polysilicon layer, and a nitride layer on asemiconductor substrate having an active region and a isolation layerdefining the active region, wherein the at least one first recess isformed in the active region of the semiconductor substrate; defining asecond recess in the active region by etching the nitride layer; forminga metal nitride layer in the second recess such that a two-dimensionalcross-sectional profile of the metal nitride layer formed in the secondrecess substantially resemble the shape of U; forming a metal layer onthe metal nitride layer filling the second recess; forming a hard masklayer on the nitride layer, the metal nitride layer, and the metallayer; and forming a metal gate by etching the nitride layer, thepolysilicon layer and the gate oxide layer using the hard mask layer asan etch barrier.

According to another aspect of the present invention, the method furthercomprises the step of defining a recess on a portion of the activeregion of the semiconductor substrate at which the gate is to be formedbefore forming the gate oxide layer on the semiconductor substrate.

According to another aspect of the present invention, the nitride layeris formed in the thickness of 300˜700 Å.

According to another aspect of the present invention, the recess isdefined to have a width which is less than that of a gate which isdesired to be formed.

According to another aspect of the present invention, the step offorming a metal nitride layer in the recess in the shape of U and then ametal layer to bury the recess comprises the sub-steps of forming themetal nitride layer on the nitride layer including the recess to auniform thickness; forming the metal layer on the metal nitride layer tobury the recess; and CMPing the metal layer and the metal nitride layerto expose the nitride layer.

According to another aspect of the present invention, the metal nitridelayer comprises a tungsten nitride layer and the metal layer comprises atungsten layer.

According to another aspect of the present invention, the tungstennitride layer is formed in the thickness of 50˜100 Å.

According to another aspect of the present invention, the tungsten layeris formed in the thickness of 500˜1,000 Å.

According to another aspect of the present invention, the method furthercomprises the step of conducting a gate re-oxidation process afterforming the metal gate.

According to still another aspect of the present invention, the gatere-oxidation process is conducted such that a re-oxidation layer havinga thickness of 30˜100 Å is formed on the etched polysilicon layer andgate oxide layer and a surface of the active region of the substrate.

According to yet still another aspect of the present invention, themethod further comprises the step of forming source and drain regions inthe surface of the active region of the substrate at both sides of themetal gate after conducting the gate re-oxidation process.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects, and other features and advantages of the presentinvention will become more apparent after a reading of the followingdetailed description when taken in conjunction with the drawings, inwhich:

FIGS. 1A through 1D are cross-sectional views for explaining the processsteps of a method of forming a recess gate according to the conventionalart; and

FIGS. 2A through 2G are cross-sectional views for explaining the processsteps of a method of manufacturing a semiconductor device in accordancewith an embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made in greater detail to a preferred embodimentof the invention, an example of which is illustrated in the accompanyingdrawings. Wherever possible, the same reference numerals will be usedthroughout the drawings and the description to refer to the same or likeparts.

FIGS. 2A through 2G are cross-sectional views for explaining the processsteps of a method for manufacturing a semiconductor device in accordancewith an embodiment of the present invention.

Referring to FIG. 2A, a semiconductor substrate 21 having an activeregion and a isolation layer 22 (which delimits the active region) isprovided. Then, an oxide layer 23 and a hard mask layer 24 aresequentially deposited on the substrate 21.

Referring to FIG. 2B, the hard mask layer 24 and the oxide layer 23 areetched to expose gate forming areas on the active region of thesubstrate 21. Next, the exposed areas of the substrate 21 is etchedusing the etched hard mask layer 24 as an etch mask, and thereby atleast one first recess 25 is formed in the gate forming areas.

Then, the hard mask layer 24 and the oxide layer 23 are sequentiallyremoved. Here, when etching the substrate 21 to define the first recess25, the isolation layer 22 may also be partially etched.

Referring to FIG. 2C, a gate oxide layer 26 is formed on the surface ofthe active region of the substrate 21 including the surfaces of thefirst recess 25. Next, a polysilicon layer 27 is formed on the gateoxide layer 26 filling the first recess 25, and then a nitride layer 28is formed on the polysilicon layer 27. Here, the nitride layer 28 isformed to a thickness in the range of 300˜700 Å.

Referring to FIG. 2D, at least one groove 29 each having a height and awidth is formed by a etching process in the nitride layer 28 above therecess 25. The width of the groove is less than the width of a gate tobe formed later (i.e., the gate 33 shown in FIG. 2F). Thereupon, after ametal nitride layer, for example, a tungsten nitride layer 30 isdeposited on the surface of the non-metal nitride layer 28 including thesurface of the groove 29. The thickness of the tungsten nitride layer inthe range of 50˜100 Å. Then, a metal layer, for example, a tungstenlayer 31 is deposited on the tungsten nitride layer 30 to a thickness inthe range of 500˜1,000 Å filling the groove 29.

Referring to FIG. 2E, by chemically and mechanically polishing(hereinafter simply referred to as “CMPing”) the metal layer 31 (e.g.,tungsten) and the metal nitride layer 30 (e.g., tungsten nitride) formedabove the height of the second recess 29 until the nitride layer 28 isexposed between two adjacent recesses 29. The second recess 29 is filledwith the metal nitride layer 30 and the metal layer 31. As shown in FIG.2E (as well as FIG. 2F), the metal nitride layer 30 formed inside thesecond recess 29 has a cross-sectional profile substantially resemblingthe shape of a “U.” As shown in FIG. 2E (and FIG. 2F), the metal layer31 fills the second recess 29 above the metal nitride layer 31 havingthe cross-sectional shape substantially resembling a “U.”

Referring to FIG. 2F, a gate hard mask 32 is formed on the metal layer31, the metal nitride layer 30, and the nitride layer 28. Thereafter,the nitride layer 28, the polysilicon layer 27, and the gate oxide layer26 are sequentially etched using the gate hard mask 32 as an etchbarrier and forms a metal gate 33. As already discussed above, the widthof the metal gate 33 is wider than the width of the second recess 29, inwhich a metal nitride layer 30 (having a substantially U-shapedcross-sectional profile) is formed. In this regard, the nitride layer 28remaining after the etch process covers up the metal nitride layer 30.This is also known as that the metal layer 30 “capped” by the nitridelayer 28.

Referring to FIG. 2G, a gate re-oxidation process is conducted for theresultant substrate 21 which is formed with the tungsten gate 33, toeliminate the damage caused due to etching, and thereby a re-oxidationlayer 34 is formed on the etched polysilicon layer 27 and gate oxidelayer 26 and the surface of the active region of the resultant substrate21 in the thickness of 30˜100 Å.

Thereafter, source and drain regions (not shown) are formed in thesurface of the active region of the substrate 21 at both sides of thetungsten gate 33 through the well-known ion implantation process. Then,a series of subsequent processes are conducted to finally manufacturethe semiconductor device according to an embodiment of the presentinvention.

As is apparent from the above description, the semiconductor device andthe method of manufacturing the same according to an embodiment of thepresent invention provide advantages in that, since a metal (ortungsten) layer is capped by a nitride layer, even when conducting agate re-oxidation process to form a conventional tungsten silicide gate,an abnormal oxidization phenomenon does not occur in the tungsten layer.As a consequence, it is not necessary to conduct a selective oxidizationprocess, which must be otherwise essentially adopted in the conventionalart to prevent the abnormal oxidization phenomenon from occurring whenforming a tungsten gate. That is to say, because the nitride layerfunctions to prevent oxidization of the tungsten layer when conductingthe gate re-oxidation process, the abnormal oxidization phenomenon doesnot occur in the tungsten layer while conducting the gate re-oxidationprocess. Therefore, in the course of mass-producing a device having atungsten gate, investment cost for manufacturing equipment, that is,selective oxidization equipment can be saved, whereby economicefficiency is improved.

Also, in the present invention, due to the fact that the metal (ortungsten) layer is capped by the nitride layer, when subsequentlyconducting the gate re-oxidation process, the contamination of tungsten,which is a detrimental defect caused in the conventional art, can beprevented. Therefore, it is possible to prevent an interfacialinsulation layer from being formed due to the intrusion of oxygenthrough the tungsten layer.

Further, in the present invention, since it is not necessary to conducta separate process for forming a gate capping nitride, which isotherwise needed in the conventional art to prevent the abnormaloxidization of tungsten in a subsequent process, a manufacturing costcan be reduced.

In the drawings and specification, there have been disclosed typicalpreferred embodiments of the invention and, although specific terms areemployed, they are used in a generic and descriptive sense only and notfor purposes of limitation, the scope of the invention being set forthin the following claims.

1. A semiconductor device comprising: a semiconductor substrate havingan active region and an isolation layer defining the active region; anda metal gate formed on the active region of the substrate, wherein themetal gate comprises: a gate oxide layer formed on a predetermined areaof the active region; a polysilicon layer formed on the gate oxidelayer; a metal nitride layer formed on the polysilicon layer, wherein across sectional profile of the metal nitride layer substantiallyresemble the shape of U; a non-metal nitride layer formed on thepolysilicon layer and only the outside sides of the metal nitride layerhaving the substantially U-shaped cross-sectional profile, wherein anupper surface of the non-metal nitride layer is coplanar with an uppersurface of the metal nitride layer; a metal layer formed inside themetal nitride layer having the substantially U-shaped cross-sectionalprofile; a hard mask layer formed on the non-metal nitride layer, themetal layer, and the metal nitride layer having the substantiallyU-shaped cross-sectional profile; and a re-oxidation layer is formed onthe sidewall of the polysilicon layer, the gate oxide and surface of theactive region.
 2. The semiconductor device of claim 1, wherein a recessis formed in the active region of the semiconductor substrate such thatthe metal gate is formed on the recess.
 3. The semiconductor device ofclaim 1, wherein the metal nitride layer is formed to surround sidesurfaces and a bottom surface of the metal layer.
 4. The semiconductordevice of claim 1, wherein the entire width of a section of the metalgate having the non-metal nitride layer outside the substantiallyU-shaped metal nitride layer and the metal layer inside thesubstantially U-shaped metal nitride layer is the same as the width of asection of the metal gate having the polysilicon layer.
 5. Thesemiconductor device of claim 1, wherein the metal nitride layercomprises tungsten nitride, wherein the metal layer comprises tungsten,and wherein the hard mask layer comprises a nitride material.
 6. Thesemiconductor device of claim 1, further comprising source and drainregions formed in the active region of the substrate at sides of themetal gate.